Lithium ion batteries as a nonaqueous electrolyte rechargeable battery are widely used in portable electronic devices, such as video cameras, mobile audio equipment, mobile phones, and notebook computers, which have been becoming smaller, lighter, and more powerful. For these electronic devices, lithium ion batteries of larger capacity and longer life have consistently been demanded. On the other hand, with the recent change in environment of use of these mobile devices, characteristics that are desired of the batteries have also been changing. In particular, batteries have recently been demanded that may be used in a stable manner even if charged at a high voltage of 4.3 V or higher, which is one of the conditions for achieving a larger battery capacity.
Under such high voltage conditions, the cathode of a lithium ion battery is prematurely deteriorated. This is due to the reaction of the cathode active material and the electrolyte to deteriorate the cathode active material, resulting in degradation of the battery life, that is, the cycle characteristics.
As one of the solutions to this problem, it is conceivable to avoid direct contact between a cathode active material and electrolyte. As means for avoiding the direct contact, there is known, for example, a method of inhibiting reaction between a cathode active material and electrolyte by providing a coating material, such as an oxide, over the surface of a cathode active material.
For example, Patent Publication 1 proposes a cathode active material coated with one or more layers of an oxide of at least one metal selected from the group consisting of Zr, Al, Si, Ti, La, Y, Sn, Zn, Mg, Ca, and Sr.
Patent Publication 2 proposes a cathode active material composed of lithium-containing composite oxide particles containing Li and at least one transition metal element selected from Ni, Co, or Mn, to which surface powder of an oxide of at least one metal element selected from Zr, Ti, Sn, Mg, Ba, Pb, Bi, Nb, Ta, Zn, Y, La, Sr, Ce, In, or Al adhere.
Patent Publication 1: JP-2001-313034-A
Patent Publication 2: JP-2012-138197-A